Police said four men were arrested in connection with the incident, which occurred just after 5pm on a stretch of road where the visiting fans’ coaches were parked up.

One witness reported seeing a Watford fan “lying on the floor, apparently unconscious, with blood on his face … Friends around him were crying and shouting for people to help and call an ambulance.”

It comes a month after the Metropolitan police described fighting that broke out before Everton’s FA Cup match at Millwall as “some of the most shocking football violence seen for some time”. A 27-year-old was arrested last week in connection with that incident, which left one Everton fan with “a life-changing” scar having been slashed across the face.